Agreed that the argument is a bit weak, but we would still end up with a major centralized repository for a decentralized protocol. And the changes to make Gitlab more like the proposal would probably be more work than just making the proposal a new project.
I think we would end up with multiple major repositories and many smaller ones. One of the first steps towards more decentralization would be an issue tracker that doesn't under numbers but hashes and that stores its content in a git repo (like the wiki already does). EDIT I noticed in the comments the Fossil already has this, interesting http://fossil-scm.org/index.html/tktview/3711fc7cfd21d7f8684...
